Abstract: The current prediction standard of gas emission is not applicable to steeply inclined and extra thick coal seam in the horizontal sublevel mining working face, and there is a deficiency in the prediction of gas emission in horizontal sublevel mining working face by using the method of sub-source prediction. In order to solve the above problems, the calculation method of influence coefficient of gas emission in roadway was put forward according to the law of mass conservation of gas; based on the calculation method for predicting gas emission from adjacent seam, the mathematical expression for predicting the gas emission from the lower part of the mining section was established, a method for predicting gas emission from horizontal sublevel mining working face of steeply inclined and extra thick coal seam was developed, and the field application was carried out. The results show that the relative error between the predicted value and the measured value is between -15.08% and 14.97%, the average value of the absolute value of the relative error is only 6.65%, the prediction effect is good, which indicates that the method is reasonable and feasible.